1. Field of the Invention
This invention relates to shifting tools for sliding sleeve type valves used in conduits or tubing strings in oil and gas wells, and more particularly, to a shifting tool adapted for selectively and sequentially shifting a sliding sleeve to intermediate and fully open positions, and for providing a positive indication to the operator as to the position of the shifter and sleeve.
2. Description of Related Art
Sliding sleeve valves for use in oil and gas valves are well known. Sliding sleeve valves are disclosed in the prior art, for example, in U.S. Pat. Nos. 3,211,232; 3,552,718; 3,845,815; 3,874,634; and 4,280,561. Some prior art shifting tools for sliding sleeve valves are disclosed in the foregoing patents, and also in U.S. Pat. No. 4,436,152.
Sliding sleeve valves can be used to control fluid flow between a tubing string and the surrounding annulus during circulation or production. Sliding sleeve valves typically contain an inner sleeve having a port that can be selectively shifted to either permit or block fluid flow through ports in the valve body. Seals are provided between the inside wall of the valve body and the sliding sleeve to prevent fluid bypass whenever the valve is closed. Sliding sleeve valves are available in configurations that either shift down to open and up to close, or up to open and down to close. The valves are ordinarily shifted using a shifting tool that is part of a wireline-deployed tool string.
In recent years, sliding sleeve valves have become available that have three distinct positions, with an equalizing position being disposed intermediate the open and closed positions. The bodies of these valves typically comprise at least one smaller diameter equalizing port through which the tubing pressure and annulus pressure can be balanced prior to fully opening the valve. By first shifting the sliding sleeve to the equalizing position, one reduces the likelihood of wireline failure due to a pressure surge as the valve is opened. When the three position sliding sleeve valves are used with the conventional shifting tools, however, operators have sometimes encountered difficulty in sequentially positioning the sliding sleeve in the intermediate, equalizing position. If the sliding sleeve is accidentally overshifted to the fully open position without first equalizing the pressure between the annulus and the interior of the tubing, damage to the valve, wireline or tool string can still occur.
A shifting tool is therefore needed that can be used to sequentially shift the sliding sleeve of a sliding sleeve valve to the equalizing and fully open positions and that will provide a positive indication to the operator whenever the sliding sleeve is in the equalizing or fully open position, respectively.